Water hardness (i.e., magnesium and calcium) in an industrial water system can pose problems such as process inefficiencies and system shutdowns. Thus, the concentration of calcium and magnesium in an industrial water system should be carefully measured and monitored. Since hardness concentration can be quite low (e.g., ppb range), quantification of these metal cations requires a sensitive and precise method of measurement. If hardness is measured accurately, proper methods of hardness reduction can be selected (e.g., filtration, membrane purification, ion exchange, and chemical treatment), and appropriate chemical treatment dosages can be used to maintain low levels of hardness.
Spectroscopic analysis can be used to measure the concentration of calcium and magnesium in an industrial water system. However, accuracy of the method of analysis is dependent upon a number of factors. For example, operational variables such as flowrate, water pressure, and temperature can change between experimental runs, leading to inconsistent performance of instrumental pumps. In addition, the concentration of reagents can vary based on the commercial source, age, and manufacture of the reagent batch. Moreover, the background fluorescence of reagents employed can vary based on the impurity levels present in the batch. Variation of equipment components such as pumps, LEDs, and system electronics over time can erode analytical accuracy and reproducibility.
Calibration methods can be used to “zero” an instrument at the time of use to account for these variables. Preferably, the calibration method is easily executed, requires minimal human effort, and ensures instrumental accuracy and reproducibility. While many calibration methods exist, further improvement is always desirable.